Abstract
The maximum curvature of a steerable needle in soft tissue is highly sensitive to needle shaft stiffness, which has motivated use of small diameter needles in the past. However, desired needle payloads constrain minimum shaft diameters, and shearing along the needle shaft can occur at small diameters and high curvatures. We provide a new way to adjust needle shaft stiffness (thereby enhancing maximum curvature, i.e. "steerability") at diameters selected based on needle payload requirements. We propose helical dovetail laser patterning to increase needle steerability without reducing shaft diameter. Experiments in phantoms and ex vivo animal muscle, brain, liver, and inflated lung tissues demonstrate high steerability in soft tissues. These experiments use needle diameters suitable for various clinical scenarios, and which have been previously limited by steering challenges without helical dovetail patterning. We show that steerable needle targeting remains accurate with established controllers and demonstrate interventional payload delivery (brachytherapy seeds and radiofrequency ablation) through the needle. Helical dovetail patterning decouples steerability from diameter in needle design. It enables diameter to be selected based on clinical requirements rather than being carefully tuned to tissue properties. These results pave the way for new sensors and interventional tools to be integrated into high-curvature steerable needles.
Highlights
Bevel tip steerable needles can be used to accurately target desired locations in tissue and travel along curved paths that are useful for avoiding obstacles [1]–[3]
ILLUSTRATION OF SHEARING AT SMALL DIAMETERS we demonstrate experimentally that shearing can occur at small needle shaft diameters and high curvatures
This paper describes a new way to decouple needle steerability from needle shaft diameter
Summary
Bevel tip steerable needles can be used to accurately target desired locations in tissue and travel along curved paths that are useful for avoiding obstacles [1]–[3]. There are a number of other noteworthy steerable needle designs including (but not limited to) use of a curved stylet in conjunction with an outer cannula proposed in [19] and later adapted with variations in stiffness and insertion approaches by others [20], [21], a programmable bevel which eliminates the need for axial rotation [22], and shape memory alloy actuation [23], among other innovative designs which are reviewed in [11] Each of these prior steerable needle designs has its own unique strengths and weaknesses. We show that this needle is capable of delivering a variety of interventional therapies including brachytherapy seeds and thermal ablation probes, which would be too large to deliver through existing small-diameter, high-curvature needles
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